More than 200 small earthquakes were reported Tuesday near Coso Junction along U.S. 395 in Inyo County, intensifying a series of temblors that have struck over the last two weeks.
The U.S. Geological Survey said the biggest of the quakes, registering magnitudes of 4.9 and 4.7, occurred at 5:07 and 5:59 a.m., respectively, but about 20 quakes per hour were recorded for nine hours. Scientists call such a sequence a quake swarm.
The quakes, including 10 registering magnitudes between 3.0 and 4.0, were centered four miles southeast of Coso Junction, close to an area pockmarked with the cinder cones of volcanic eruptions that occurred long ago.
The area north of the Little Lake ghost town is rural, and no damage or injuries were reported. In urban areas, a 4.9 quake is normally above the threshold for minor damage.
The quakes were felt mildly in northern parts of the Los Angeles Basin.
Caltech seismologist Egill Hauksson said some scientists think it is possible that quakes in the area in early 1992 triggered the magnitude 7.3 Landers quake of June 28, 1992--farther south along what is known as the Eastern California Shear Zone--so these quakes are monitored carefully.
There have been numerous quake swarms in the vicinity, with the largest temblor in recent years being a magnitude 5.8 on Sept. 20, 1995.
Hauksson said a pool of magma, or molten lava, probably lies about four miles under the surface of a geothermal area being developed about 10 miles northeast of where the present quakes are occurring.
But there is no indication that a volcanic eruption is likely in the near future, said Hauksson and Wendell Duffield of the Geological Survey's Flagstaff, Ariz., office, who has studied the area.
Tuesday's quakes were mostly shallow, possibly less than four miles deep.
Residents and workers in the area took them in stride. "Mostly, it was a lot of noise," said Nancy Lutsey, a cashier at Coso Junction's general store. "It was a couple of good jolts, that's it."
Coso Junction is about 140 miles north of Los Angeles.